We will determine the incidence of fatal coronary artery disease (CAD) and second primary malignancies (SPM) following treatment for breast cancer, and will determine whether there is variation in these incidences by modality of treatment. In the literature, the relationship between irradiation and subsequent CAD is unknown. Radiation therapy is clearly implicated in the induction of SPM, but specifics of the dose and time relationships remain undertain. Our study population will consist of 2,750 women who were treated, either with mastectomy alone or with mastectomy followed by irradiation, at Massachusetts General Hospital or at Southwood community Hospital (formerly Pondville State Cancer Hospital) from 1960 through 1971. Detailed data on radiation technique and on a variety of risk indicators will be collected. Two methods of statistical analysis will be employed: contingency tables with stratification and the Cox proportional hazard model. Two sorts of basic comparisons will be made: women who were irradiated will be compared with those who were not, and women who were treated to the left chest will be compared with those treated to the right chest. The left versus right comparison is attractive because it will allow identification of a group of women who were "randomized" to receive heart irradiation. We will determine the relative risk of CAD and SPM subsequent to irradiation and will define the possible dose modification of other risk indicators such as cigarette smoking and blood pressure. The results of this research should have immediate application in the rational design of cancer therapy regimens.